This invention relates to a method and apparatus for processing a spent ion exchange resin, particularly a radioactive spent ion exchange resin generated in a nuclear power plant or the like.
The methods of reducing the volume of the spent ion exchange resin (waste resin) and converting it into inorganic matters can be broadly classified into a wet process typified by an acid decomposition method and a pyrolytic drying process typified by a fluidized bed method.
The wet process involves a problem in that after the waste resin is subjected to a decomposition treatment, a radioactive waste liquor containing decomposition residues must be again processed by any suitable means such as concentration by evaporation.
A fluidized bed method is a typical example of the dry process, wherein the waste resin is burnt by use of a fluidized bed, as illustrated in Japanese Patent Laid-Open No. 12400/1982, for example.
Though the dry process is free from the problems of the wet process, the following problems are encountered when the fluidized bed method as a typical example of the dry process is employed.
(1) The scattering quantity of the residue and ratioactive substances is great. In other words, since the waste resin is dispersed and burnt under a flowing gas, the residue and radioactive substances are entrained by the decomposition gas (exhaust gas) and scattered. Therefore, the load to a filter for processing the exhaust gas becomes great.
(2) When the waste resin is burnt, harmful decomposition gases such as oxide gases (SO.sub.x), (NO.sub.x) and the like are generated. For this reason, exhaust gas processing by means of an alkali scrubber or the like becomes necessary, but the quantity of the exhaust gas to be processed is enormous. In other words, in accordance with the fluidized bed method, air containing oxygen from three to five times the chemical equivalent must be supplied, and hence the quantity of the exhaust gas is increased so much.
(3) Not only the residue but also the secondary waste generated as a result of processing the exhaust gas, such as NaNO.sub.3 and Na.sub.2 SO.sub.4, incorporate into the radioactive substances of radioactive nuclides. And these are added to the radioactive wastes, thereby reducing the volume reduction ratio.
In other words, when 1 kg of the waste resin is burnt in the fluidized bed, the decomposition residue reaches several percents (about 3 g) and at the same time, about 0.7 kg of radioactive waste is generated. If this waste is subjected to volume reduction and is pelletized by the existing equipment for processing the radioactive waste, the volume reduction ratio is nothing but 1/4.
H.sub.2 O and CO.sub.2 are also generated as the radioactive waste in quantities of 0.4 kg and 2.3 kg, respectively. If the quantity of the residue generated is 0.03 kg, the content of the sulfur and nitrogen compounds contained in the secondary radioactive waste generated by pyrolysis of the waste resin is 18 wt %.
When 1 kg of the cation exchange resin alone is pyrolyzed as the waste resin, the content described above is 24 wt %, and when 1 kg of the anion exchange resin alone is pyrolyzed, the content is 9 wt %. In other words, the content becomes worst when the cation exchange resin alone is pyrolyzed and the value is as great as 24 wt %. The reduction of secondary radioactive waste is desirable further carried out from the aspect of the reduction of the generation quantity of the radioactive waste.
(4) Since combustion is effected in single stage of the oxidizing atmosphere at a pyrolyzing temperature in the range of from 600.degree. to 900.degree. C., the furnace material will be deteriorated during use for an extended period.
(5) The problem common to the conventional techniques of reducing the volume of the waste resin and converting it into the inorganic matters is that the system for said conversion and that for solidifying the decomposition residue are separate from each other, so that the systems become complicated and the operators or workers are likely to be exposed to the radioactivity in the handling of the waste resin.